Two fiber support with single optical amplifier

ABSTRACT

An optical amplifier for a 4-fiber system having two inputs and outputs is provided that makes use of a single amplifier rather than two separate amplifiers. The optical amplifier node makes use of an interleaver before and after the single amplifier to demultiplex and multiplex even and odd channel signals traveling in opposite directions. The optical amplifier node can be combined with other like amplifier nodes to provide more complex amplifier solutions at reduced costs due to the need for only half of the typical number of amplifiers. The optical amplifier node can also be combined with, e.g., variable optical attenuators, L/C filters, channel add/drop, and dispersion compensation modules to modify the optical signals as desired.

FIELD OF THE INVENTION

The invention relates to an optical amplifier, and more particularlyrelates to the use of a single optical amplifier to amplify signalstraveling through a plurality of fibers.

BACKGROUND OF THE INVENTION

A conventional 4-fiber optical amplifier is illustrated in FIG. 1. Theoptical amplifier node 10 has a first input fiber 12 that couples with afirst variable optical attenuator 18 for attenuating optical signalscarried over the first input fiber 12. The variable optical attenuator18 can be either before or after an amplifier 14. In this instance, theoptical signals leave the optical attenuator 18 and pass to theamplifier 14. The resulting amplified optical signals exit the amplifier14 and pass to a first output fiber 16. A second input fiber 20 carriesoptical signals entering from a second direction opposite the directionof the signals in the first input fiber 12. The second input fiber 20couples to a second variable optical attenuator 26. The attenuatedoptical signals pass to a second amplifier 22. The amplified output fromthe second amplifier 22 passes to the second output fiber 24.

In this conventional optical amplifier node, each signal path requires aseparate optical amplifier. As optical amplifiers are costly, the use ofmultiple amplifiers poses a significant cost for constructing opticalnetworks.

SUMMARY OF THE INVENTION

There is a need for an optical amplifier node that uses a singleamplifier to amplify signals travelling in different directions. Thepresent invention is directed toward further solutions. In accordancewith aspects of the present invention, an optical amplifier node has afirst and second input fiber in communication with a first interleaver.A first amplifier is also in communication with the first interleaver. Asecond interleaver is in communication with the first amplifier, andfirst and second output fibers are in communication with the secondinterleaver. The first and second input fibers, in accordance with oneaspect of the present invention, each support signal traffic travelingin opposite directions.

The optical interleaver can take an optical signal and separate it into,e.g., odd and even channels when the optical signal passes through theinterleaver in a first direction. A number of odd and even channels canalso pass through the interleaver in a second direction, opposite to thefirst direction, and the interleaver will combine those odd and evensignals into a combined signal. The interleaver can separate and combineother types of signals, and in different ways including by bit, byte,signal, channel, wavelength, band, and the like.

The optical amplifier node, in accordance with a further aspect of thepresent invention, has a first variable optical attenuator incommunication with one of the first input fiber and the first outputfiber. The optical amplifier node further has a second variable opticalattenuator in communication with one of the second input fiber and thesecond output fiber.

In addition, the optical amplifier node can have a second amplifier incommunication with an L/C splitter and L/C combiner. The function of theL/C splitter is to separate two wavelength bands spatially into twoseparate fibers. The C band is commonly defined as 1530 nm to 1565 nm,while the L band is commonly defined as 1570 nm to 1610 nm. The LICcombiner takes two separate C and L wavelength bands, and combines themaccordingly.

Prior to a signal reaching the input of the optical amplifier node, thesignal can travel through a multiplexor in communication with the firstinterleaver. A dispersion compensation module can be positioned on thecommunication path between the multiplexor and the first interleaver. Adispersion compensation module can also be positioned on thecommunication path between the first interleaver and the first amplifierto compensate for dispersion. Alternatively, the optical amplifier nodecan have a first amplifier that is a multistage access amplifier with anintegrated dispersion compensation module.

The optical amplifier node, in accordance with other aspects of thepresent invention, includes a demultiplexor in communication with thesecond interleaver off of the output fiber. A dispersion compensationmodule can be positioned on the communication path between thedemultiplexor and the second interleaver.

Aspects of the present invention further include a method of amplifyingan optical signal. The method begins with routing signal traffictraveling originating from opposite directions through a firstinterleaver to interleave each of the opposing traveling signals into acombined signal. The method continues with routing the combined signalthrough a first amplifier to amplify that signal. The combined signal isthen routed through a second interleaver to separate the combined signalinto the distinct signals traveling in opposite directions. The methodcan further include the step of routing the signals originating fromopposite directions through variable optical attenuators. Alternatively,the method can include the step of routing the combined signal throughan L/C splitter, a second amplifier, and an L/C combiner.

The signals traveling in opposite directions can travel through one of amultiplexor and a demultiplexor at points external to the amplifier. Themethod can further include the step of routing the combined signalthrough a dispersion compensation module, either as a stand alonemodule, or as a part of a mid-stage access amplifier having a dispersioncompensation module built within.

The optical amplifier node, according to still another aspect of thepresent invention, can include a first and second input fiber incommunication with a first interleaver. The optical amplifier nodefurther includes a first amplifier in communication with the firstinterleaver. A second interleaver is in communication with the firstamplifier. At least two dispersion compensation modules are incommunication with the second interleaver. A third interleaver is incommunication with at least two dispersion compensation modules. Asecond amplifier is in communication with the third interleaver. Afourth interleaver is in communication with the second amplifier, and afirst and second output fiber are in communication with the fourthinterleaver.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned features and advantages, and other features andaspects of the present invention, will become better understood withregard to the following description and accompanying drawings, wherein:

FIG. 1 is a diagrammatic illustration of a known optical amplifier node;

FIG. 2 is a diagrammatic illustration of an optical amplifier nodeaccording to a first embodiment of the present invention;

FIG. 3 is a diagrammatic illustration of an optical amplifier nodeaccording to a second embodiment of the present invention;

FIG. 4 is a diagrammatic illustration of an optical amplifier nodeaccording to a third embodiment of the present invention;

FIG. 5 is a diagrammatic illustration of an optical amplifier nodeaccording to a fourth embodiment of the present invention;

FIG. 6 is a diagrammatic illustration of an optical amplifier nodeaccording to a fifth embodiment of the present invention;

FIG. 7 is a diagrammatic illustration of an optical amplifier nodeaccording to a sixth embodiment of the present invention; and

FIG. 8 is a diagrammatic illustration of an optical amplifier nodeaccording to a seventh embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The illustrative embodiments of the present invention generally relateto the use of a single amplifier to amplify signals from a 4-fibersystem (two input fibers and two output fibers). Prior technologyutilizes a single amplifier for each fiber, which results in twoamplifiers forming an amplifier node for a 4-fiber system. The presentinvention utilizes an optical interleaver to multiplex an odd channelsignal from a fiber containing signal traffic traveling in a firstdirection with an even channel signal from a fiber containing signaltraffic traveling in a second direction, into a single optical fiber.The single optical fiber then passes through the optical amplifier. Inthe output portion of the optical amplifier, the single optical signalis demultiplexed with another interleaver. The four fibers into thesystem, the two inputs and two outputs, are then spatially directed tothe correct routing.

FIGS. 2 through 8 wherein like parts are designated by like referencenumerals throughout, illustrate example embodiments of an opticalamplifier node according to the present invention. Although the presentinvention will be described with reference to the example embodimentsillustrated in the figures, it should be understood that manyalternative forms can embody the present invention. One of ordinaryskill in the art will additionally appreciate different ways to alterthe parameters of the embodiments disclosed, such as the size, shape, ortype of elements or materials, in a manner still in keeping with thespirit and scope of the present invention.

FIG. 2 illustrates an optical amplifier node 30 according to oneembodiment of the present invention. There is an even channel signalthat travels through a first input fiber 32 into a first interleaver 36.The even channel signal can be an odd channel signal, so long as thesignal traveling through a second input fiber 34 is an even channelsignal.

The even/odd channel separation is intended to indicate a signal beingseparated in an alternating fashion, e.g., every other sub-component ofthe signal is removed from the first signal to form two separatesignals. The even/odd convention is utilized throughout this descriptionfor illustrative purposes only, and one of ordinary skill in the artwill understand that the signals can be separated in any number ofdifferent manners, such as by bit, byte, wavelength, signal, band, andthe like. The inventors anticipate that each of these different signalseparation techniques are intended where appropriate in eachillustrative instance of the even/odd channel separation technique asutilized throughout this description.

It should also be noted that each channel signal is associated with aseparate wavelength, and a single fiber can carry a relatively largenumber of channels concurrently at different wavelengths.

A variable optical attenuator 38 is provided on the first input fiber 32to attenuate the even channel signal as desired. If there is no need forattenuation, this optical attenuator 38 is not required as is understoodby one of ordinary skill in the art.

The variable optical attenuators illustrated throughout FIGS. 2-8 areshown prior to the interleaver and amplifier combinations, and after theinterleaver and amplifier combinations. The applicants intend for thevariable optical attenuators to be placed in either or both locations inall illustrated embodiments (although the variable optical attenuatorsare typically illustrated in one or the other locations herein), oralternatively in intermediate locations between interleavers, asrequired by the particular implementations.

An odd channel signal enters the optical amplifier node 30 through thesecond input fiber 34. The odd channel signal travels in the oppositedirection to the even channel signal. The odd channel signal enters thefirst interleaver 36 after passing through a variable optical attenuator40. Again, this optical attenuator 40 is only required if attenuation ofthe signal is necessary.

A first interleaver 36 combines each of the even and odd channel signalsinto a combined signal, which then exits the first interleaver 36through a connecting fiber 42. The connecting fiber 42 routes thecombined signal to a first amplifier 44, which amplifies the signal.

The single amplified signal then leaves the amplifier 44 and travelsthrough the connecting fiber 46 to a second interleaver 48. The secondinterleaver 48 splits the amplified signal into the respective even andodd channel signals. The even channel signal propogates in the samedirection as it entered the optical amplifier node 30 by exiting throughthe first output fiber 50. The odd channel signal, likewise, propagatesin its original direction by exiting the second interleaver 48 throughthe second output fiber 52.

FIG. 3 illustrates another embodiment of an optical amplifier node 54.The illustrated embodiment combines two of the arrangements shown inFIG. 2. The embodiment shown in FIG. 3 has a first input fiber 32through which the even channel signal enters and the second input fiber34 through which the odd channel signal enters. Again, these even andodd designations can be reversed as understood by one of ordinary skillin the art.

The signals combined in the first interleaver 36 travel through theconnecting fiber 42 to the amplifier 44. The amplified combined signalsexit the amplifier 44 and travel along the connecting fiber 46 to thesecond interleaver 48, where the signals are separated. At this point,the even channel signal travels through a first dispersion compensationmodule 56, while the odd channel signal travels through a seconddispersion compensation module 58. Both signals are then combined in athird interleaver 37. The combined signals travel along a connectingfiber 43, through a second amplifier 45, along a connecting fiber 47, toa fourth interleaver 49. Upon exiting the fourth interleaver 49, theeven channel signal passes through a variable optical attenuator 38placed on the output fiber 50, while the odd channel signal passesthrough a variable optical attenuator 40 and passes through the secondoutput fiber 52.

The optical attenuators 38 and 40 of FIG. 3 can be placed and attenuatethe optical signals prior to entry into the amplifier or amplifiers, oneither side of the dispersion compensation modules 56 and 58, or theoptical signals can pass through the optical attenuators 38 and 40subsequent to exiting the amplifier or amplifiers.

FIG. 4 illustrates still another embodiment of an optical amplifier node60 according to aspects of the present invention. An even channel signalenters through the first input fiber 32 into the first interleaver 36,while the odd channel signal enters through the second input fiber 34into the first interleaver 36. It should be noted that the even and oddchannel designations are merely for illustrative purposes as being splitsignals that can be combined and split by the interleavers 36, 37, 48,and 49.

The combined signal propagates through the connecting fiber 42, theamplifier 44, the connecting fiber 46, and the second interleaver 48.The second interleaver 48 splits the combined signal into the respectiveeven channel and odd channel signals. The even channel signals proceedthrough a first dispersion compensation module 56, and then passesthrough a channel drop 62 and a channel add 64. Meanwhile, the oddchannel signal passes through a dispersion compensation module 58 and aseparate channel drop 62 and channel add 64. The even and odd signalsonce again combine in the third interleaver 37 after passing through thechannel drops 62 and channel adds 64.

The channel drop 64 enables the amplifier node 60 to remove predeterminechannel signals from a stream of signals passing through the node 60.The channel add 64, likewise enables the amplifier node 60 to addpredetermined channel signals to a stream of signals passing through thenode 60.

The combined signals exit the third interleaver 37 along the connectingfiber 43 to the amplifier 45. The amplifier 45 amplifies the combinedsignal, and the amplified combined signal exits along the connectingfiber 47 to the fourth interleaver 49, where the combined signal is onceagain split into the even and odd channel signals. The even channelsignal exits the interleaver 49, passes through the variable opticalattenuator 38 and propagates along the first output fiber 50. The evenchannel signal exits the interleaver 49, passes through the variableoptical attenuator 40, and propagates along the second output fiber 52.

In still another embodiment of the invention, as illustrated in FIG. 5,another optical amplifier node 66 is provided. An even channel signalenters through the first input fiber 32 into the first interleaver 36.An odd channel signal enters through the second input fiber 34 into thefirst interleaver 36. Again, the even and odd channel designations areintended merely to illustrate a split signal that can be combined andsplit by the particular interleaver technology employed as previouslydetailed.

The first interleaver 36 combines the even and odd channel signals intoa combined signal, which exits along the connecting path 42. Thecombined signal then enters an L/C splitter 70, whereupon the signalsplits and a first portion of the signal travels along connecting fiber72 to a second amplifier 68 while a second portion of the signalpropagates along the connecting fiber 42 to the first amplifier 44. Thefirst and second signal portions recombine at an L/C combiner 76 andenter the second interleaver 48 as a combined signal. The secondinterleaver 48 once again separates the combined signal into therespective even and odd channels, which exit the second interleaver 48along the first output fiber 50 and the second output fiber 52.

FIG. 6 illustrates still another optical amplifier node 78. In thisoptical amplifier node 78, e.g., the even channel signal first passesthrough a multiplexor 80 prior to passing through a dispersioncompensation module 82 on the first input fiber 32, which leads to thefirst interleaver 36. The, e.g., odd channel signal enters directlythrough the second input fiber 34 into the first interleaver 36. Thefirst interleaver 36 combines the even and odd channel signals into acombined signal and the combined signal exits the first interleaver 36along the connecting fiber 42. The amplifier 44 amplifies the combinedsignal and the amplified combined signal travels along the connectingfiber 46 to the second interleaver 48. The second interleaver 48separates the combined signal into even and odd channel signals. Theeven channel signal exits along the first output fiber 50, while the oddchannel signal exits along the second output fiber 52, through adispersion compensation module 84, and into a demultiplexor 86.

In an alternative arrangement to that of FIG. 6, an additional opticalamplifier node 88 is illustrated in FIG. 7. The, e.g., even channelsignal passes through the multiplexor 80 and enters the firstinterleaver 36 along the first input fiber 32. The, e.g., odd channelsignal enters along the second input fiber 34 into the first interleaver36. The first interleaver 36 combines the even and odd channel signals,and the combined signal exits along the connecting fiber 42 and throughthe dispersion compensation module 90. The combined signal is thenamplified in the first amplifier 44, travels through the connectingfiber 46, and enters the second interleaver 48. The second interleaver48 separates the signals into even and odd channels. The even channelexits on the first output fiber 50, while the odd channel exits throughthe second output fiber 52 and into the demultiplexor 86.

FIG. 8 illustrates still another embodiment of the present invention. Anoptical amplifier node 92 has an, e.g., even channel signal enteringthrough the multiplexor 80, along the first input fiber 32, and into thefirst interleaver 36. The, e.g., odd channel signal enters the firstinterleaver 36 through the second input fiber 34. The first interleaver36 combines the even and odd channels into a combined signal, whichtravels along the connecting fiber 42 to a mid-stage access amplifier 94with a dispersion compensation module 96 built within. The amplifiedcombined signal exits along the connecting fiber 46 and enters thesecond interleaver 48. The second interleaver 48 separates the even andodd channels, and the even channel exits along the first output fiber50. The odd channel signal exits through the second output fiber 52, andenters the demultiplexor 86.

There are many features and advantages associated with aspects of thepresent invention. Embodiments of the present invention provideamplification of optical signals traveling in opposite directions usinga single amplifier, thereby reducing the required number of amplifiersto perform signal amplification. The signals entering the amplifier nodeof the present invention must contain one collection of signals, e.g.,odd channels, traveling in one direction and another collection ofsignals, e.g., even channels traveling in the other direction. Thechannel signals can be traveling on for example, 200 GHz or 100 GHzchannel spacing. There is only one gain available for the traffictraveling in both directions because there is only one amplifier. Theintroduction of a variable optical attenuator either before or after theamplifier enables two different effective gains. The optical performanceof the amplifier node of the present invention has the samefunctionality as an amplifier node having two individual non-multiplexedamplifiers, one on each fiber, although the present invention requiresonly half the number of amplifiers, thus substantially reducing costsassociated with forming the networked structures.

Numerous modifications and alternative embodiments of the invention willbe apparent to those skilled in the art in view of the foregoingdescription. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the best mode for carrying out the invention. Details of thestructure may vary substantially without departing from the spirit ofthe invention, and exclusive use of all modifications that come withinthe scope of the appended claims is reserved. It is intended that theinvention be limited only to the extent required by the appended claimsand the applicable rules of law.

What is claimed is:
 1. An optical amplifier node, comprising: a firstinterleaver; a first and second input in communication with a firstinterleaver; a first amplifier in communication with said firstinterleaver; a second interleaver in communication with said firstamplifier; a first and second output in communication with said secondinterleaver; and a first variable optical attenuator in communicationwith one of said first input and said first output.
 2. The opticalamplifier node of claim 1, wherein a second variable optical attenuatoris in communication with one of said second input and said secondoutput.
 3. An optical amplifier node, comprising: a first interleaver; afirst and second input in communication with a first interleaver; afirst amplifier in communication with said first interleaver; a secondinterleaver in communication with said first amplifier; a first andsecond output in communication with said second interleaver; and atleast one dispersion compensation module in communication with said atleast one of first and second outputs.
 4. The optical amplifier node ofclaim 3, further comprising at least one channel drop device incommunication with one of said second interleaver and said at least onedispersion compensation module.
 5. The optical amplifier node of claim3, further comprising at least one channel add device in communicationwith one of said second interleaver and said at least one dispersioncompensation module.
 6. The optical amplifier node of claim 3, furthercomprising a third interleaver in communication with said first andsecond dispersion compensation modules.
 7. The optical amplifier node ofclaim 6, further comprising a second amplifier in communication withsaid third interleaver.
 8. The optical amplifier node of claim 7,further comprising a fourth interleaver in communication with saidsecond amplifier.
 9. The optical amplifier node of claim 8, furthercomprising at least one variable optical attenuator in communicationwith said fourth interleaver.
 10. An optical amplifier node, comprising:a first interleaver; a first and second input in communication with afirst interleaver; a first amplifier in communication with said firstinterleaver; a second interleaver in communication with said firstamplifier; a first and second output in communication with said secondinterleaver; and second amplifier in communication with an L/C splitterand an L/C combiner.
 11. An optical amplifier node, comprising: a firstinterleaver; a first and second input in communication with a firstinterleaver; a first amplifier in communication with said firstinterleaver; a second interleaver in communication with said firstamplifier; a first and second output in communication with said secondinterleaver; a multiplexor in communication with said first interleaver;and a dispersion compensation module positioned on the communicationpath between said multiplexor and said first interleaver.
 12. Theoptical amplifier node of claim 11, further comprising a dispersioncompensation module positioned on the communication path between saidfirst interleaver and said first amplifier.
 13. The optical amplifiernode of claim 11, wherein said first amplifier is a mid-stage accessamplifier having a dispersion compensation module.
 14. An opticalamplifier node, comprising: a first interleaver; a first and secondinput in communication with a first interleaver; a first amplifier incommunication with said first interleaver; a second interleaver incommunication with said first amplifier; a first and second output incommunication with said second interleaver; a demultiplexor incommunication with said second interleaver; and a dispersioncompensation module positioned on the communication path between saiddemultiplexor and said second interleaver.
 15. The optical amplifiernode of claim 14, further comprising a dispersion compensation modulepositioned on the communication path between said first interleaver andsaid first amplifier.
 16. The optical amplifier node of claim 14,wherein said first amplifier is a mid-stage access amplifier having adispersion compensation module.
 17. A method of amplifying an opticalsignal, comprising the steps of: routing signals traveling in oppositedirections through said first interleaver to interleaf said opposingtraveling signals into a combined signal; routing said combined signalthrough a first amplifier to amplify said combined signal; routing saidcombined signal through a second interleaver to separate said combinedsignal into separate signals; and routing one of said signals travelingin opposite directions, and said separate signals, through variableoptical attenuators.
 18. A method of amplifying an optical signal,comprising the steps of: routing signals traveling in oppositedirections through said first interleaver to interleaf said opposingtraveling signals into a combined signal; routing said combined signalthrough a first amplifier to amplify said combined signal; routing saidcombined signal through a second interleaver to separate said combinedsignal into separate signals; and routing said separate signals throughat least one dispersion compensation module.
 19. A method of amplifyingan optical signal, comprising the steps of: routing signals traveling inopposite directions through said first interleaver to interleaf saidopposing traveling signals into a combined signal; routing said combinedsignal through a first amplifier to amplify said combined signal;routing said combined signal through a second interleaver to separatesaid combined signal into separate signals; and routing said separatesignals through at least one channel add device.
 20. A method ofamplifying an optical signal, comprising the steps of: routing signalstraveling in opposite directions through said first interleaver tointerleaf said opposing traveling signals into a combined signal;routing said combined signal through a first amplifier to amplify saidcombined signal; routing said combined signal through a secondinterleaver to separate said combined signal into separate signals; androuting said separate signals through at least one channel drop device.21. A method of amplifying an optical signal, comprising the steps of:routing signals traveling in opposite directions through said firstinterleaver to interleaf said opposing traveling signals into a combinedsignal; routing said combined signal through a first amplifier toamplify said combined signal; routing said combined signal through asecond interleaver to separate said combined signal into separatesignals; and routing said combined signal through an L/C splitter, asecond amplifier, and an L/C combiner.
 22. A method of amplifying anoptical signal, comprising the steps of: routing signals traveling inopposite directions through said first interleaver to interleaf saidopposing traveling signals into a combined signal; routing said combinedsignal through a first amplifier to amplify said combined signal;routing said combined signal through a second interleaver to separatesaid combined signal into separate signals; and routing said first andsecond signals through a first and second dispersion compensationmodules respectively.
 23. A method of amplifying an optical signal,comprising the steps of: routing signals traveling in oppositedirections through said first interleaver to interleaf said opposingtraveling signals into a combined signal; routing said combined signalthrough a first amplifier to amplify said combined signal; routing saidcombined signal through a second interleaver to separate said combinedsignal into separate signals; and routing said combined signal through adispersion compensation module.
 24. A method of amplifying an opticalsignal, comprising the steps of: routing signals traveling in oppositedirections through said first interleaver to interleaf said opposingtraveling signals into a combined signal; routing said combined signalthrough a first amplifier to amplify said combined signal; routing saidcombined signal through a second interleaver to separate said combinedsignal into separate signals; and routing said combined signal throughsaid first amplifier includes routing said signal through a mid-stageaccess amplifier having a dispersion compensation module.
 25. An opticalamplifier node, comprising: a first and second input in communicationwith a first interleaver; a first amplifier in communication with saidfirst interleaver; a second interleaver in communication with said firstamplifier; at least two dispersion compensation modules in communicationwith said second interleaver; a third interleaver in communication withsaid at least two dispersion compensation modules; a second amplifier incommunication with said third interleaver; a fourth interleaver incommunication with said second amplifier; and a first and second outputin communication with said fourth interleaver.
 26. The optical amplifiernode according to claim 25, further comprising a variable opticalattenuator positioned on said first and second outputs.
 27. The opticalamplifier node according to claim 25, further comprising at least onechannel add device in communication with said third interleaver.
 28. Theoptical amplifier node according to claim 25, further comprising atleast one channel drop device in communication with said thirdinterleaver.